Merge topic 'ffmpeg-deprecated-calls'

b8da15a0 IO/FFMPEG: avoid deprecated `avcodec_close`
c2bd786a vtkFFMPEGVideoSource: free the context itself as well

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Reviewed-by: Mathieu Westphal (Kitware) <mathieu.westphal@kitware.com>
Merge-request: !11856